


Cross That Line

by drabbletale



Series: Fellcest Drabbles [4]
Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, M/M, slight dubcon
Language: English
Status: Completed
Published: 2018-01-05
Updated: 2018-01-05
Packaged: 2019-02-28 13:31:36
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,026
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13272447
Author URL: https://archiveofourown.org/users/drabbletale/pseuds/drabbletale
Summary: “Do you love me?”The words hit Sans’ heart like a blast and his reply died in his throat several times before he could manage to speak. “o-of course I do… you’re my… my brother.”“I love you too, brother.” He set a hand on Sans’ shoulder, running his fingers through the fur lining of his hood. “Very much so.”





	Cross That Line

Papyrus wasn’t happy. It took only seconds of walking into the house for Red to notice it. The very air of their shared home was heavy with… tension. 

 _So much for going to Grillby’s_. “uh… boss?” Sans called out carefully, checking the kitchen when there was no answer.

With the lower level being empty, he shrugged it off and teleported straight to his room. Nearly, but not quite, teleporting straight into his brother. His soul plummeted. “pa-… boss! shit, you scared the hell out of me!”

Papyrus was faced away from him, his head slightly lowered as he looked at something in his hands. There was a silence that passed between them, Papyrus standing completely still and Sans staring at his back. It was unnerving, but he wasn’t quite motivated to irritate the situation any further.

“Sans.”

“y-yes boss?”

“Do you love me?”

The words hit Sans’ heart like a blast and his reply died in his throat several times before he could manage to speak. “o-of course I do… you’re my… my brother.” He mumbled, shifting on his feet and shoving his hands in his pockets. “what’s goin’ on, boss? what’s that you’re holding?”

Papyrus sighed and shoved whatever it was into the pocket of his pants and turned around to stare down at Sans. “I love you too,  _brother._ ” He set a hand on Sans’ shoulder, running his fingers through the fur lining of his hood. “Very much so.”

“yeah, i know…” Sans felt himself shrink under the attention, when usually he would have preened with it. Something was very wrong here and it was the _tone_  of the attention that told him that.

“Sans… it’s crucial we get this dealt with.”

“what are ya talking about?”

“This… thing… between us.” Papyrus’ hand lifted to trace a gentle line along the edge of Sans’ jaw, ending at his chin. He tilted his brother’s face up to him and leaned in a little. “I know you think about me, Sans. When you’re in heat, your entire fist up inside of you.”

The eye lights disappeared from Sans’ sockets, his face flushing a bright red as he trembled in his brother’s hand. “y-you…”

“I watched you, Sans. I heard your voice and…” He patted his back pocket. “Figured out where my  _dirty laundry_  has been running off to.” Papyrus closed the gap between them, pressing his hardness into Sans’ lower ribs. Sans cleared his throat and took a step back, his brother’s hand lingering in the air where it had been touching him. “Sans?”

“b-boss… papyrus… i… i know i shouldn’t have… but…”

“Sans, you’re not paying attention.” Papyrus crossed his arms, his hands clenching at his upper-arms. “I want this too. We can-”

“no. no pap, we can’t. i…” Sans took a deep breath and finally opened his eyes to look over his brother again. “i know this sounds… wrong… by what you’ve seen and uh… heard… but pap. we’re brothers. the only reason i did this stuff was because… i mean, we’re the only skeletons around and it’s just genetics. i never meant for you to f-find out about this shit. i’m disgustin’, i know… but it was just to… get off… there’s nothin’ actually… we can’t… p-pap, please…”

Papyrus was listening too intently to Sans’ rambling and the shorter skeleton shifted nervously under the scrutiny. “Genetics indeed.”

“ah… i meant uh… instincts. you know, like, the draw for another skeleton, but that’s all… it’s somethin’ we can’t just give in to…”

“And why not?” Sans sputtered, twisting his hands in front of him, but not giving any real reply. “People already want us dead, brother. Any date I’ve been on has ended in death or… near death experiences.” Sans’ face dropped and he looked to the floor. “I know you’ve fucked a few times. Slutting around Snowdin. But I also know you’re just acting out of desperation.”

“boss…”

“You want  _me_. And I want you.” Papyrus growled, taking a step closer to his brother again. “There’s no point in denying what you want any more, Sans.” He had backed his brother against the door, and his hand traveled from Sans’ chest, down to slip beneath his pants. Sans’ eyes went wide and he gasped, unable to control himself as he arched into his brother’s warm hands. “You had trouble getting off, didn’t you, brother? Even in your heat, you needed more to even cum, hm?”

Sans gripped his brothers shoulders as the clawed fingers gently but firmly rubbed at his pelvic arch, forcing his magic to form the pussy he had been so frustrated with earlier in the week. He couldn’t stop his panting now, hands shaking as three of Papyrus’ fingers slipped inside him easily.

“Go fucking figure, the little slut is still worked up, a week after his heat  _supposedly_  ended.” He curved his fingers inside of his brother’s magic, causing Sans to let out a stifled moan. He started to thrust then, curving his fingers when they pushed as far in as they could go. Sans was already close, he could barely stay standing as he tried to spread his legs further for his brother.

“hnngh, p-pa… boss… please… o-oh ffffuck… aah, ahhhhhh!” He surprised Papyrus when he nearly jumped up to wrap his arms around his brother’s neck, bringing the other down to a kiss as he came hard on Papyrus’ fingers.

When he started to come down, he looked more tired than he ever had, though the magic red glow on his cheeks told Papyrus he was satiated.

Papyrus caught his brother in his arms and picked him up, taking him out of Sans’ room and into his own, where he gently laid him on the bed. Sans looked up at him tiredly, shaking hands pulling up the blankets that were handed to him.

“We’re together now, brother. No more sleeping around, okay?” Papyrus grinned as Sans nodded silently. He only looked so tired because he came so hard, he was trembling because he wasn’t used to it being so good.

Yes, now that they were together, Sans would never have to be alone. And neither would he.


End file.
